837 research outputs found
Polar cap magnetic field reversals during solar grand minima: could pores play a role?
We study the magnetic flux carried by pores located outside active regions
with sunspots and investigate their possible contribution to the reversal of
the global magnetic field of the Sun. We find that they contain a total flux of
comparable amplitude to the total magnetic flux contained in polar caps. The
pores located at distances of 40--100~Mm from the closest active region have
systematically the correct sign to contribute to the polar cap reversal. These
pores can predominantly be found in bipolar magnetic regions. We propose that
during grand minima of solar activity, such a systematic polarity trend, akin
to a weak magnetic (Babcock-Leighton-like) source term could still be operating
but was missed by the contemporary observers due to the limited resolving power
of their telescopes.Comment: 11 pages, 9 figures, accepted for publication in
Astronomy&Astrophysic
A simulation of solar convection at supergranulation scale
We present here numerical simulations of surface solar convection which cover
a box of 303.2 Mm with a resolution of
31582, which is used to investigate the dynamics of scales
larger than granulation. No structure resembling supergranulation is present;
possibly higher Reynolds numbers (i.e. higher numerical resolution), or
magnetic fields, or greater depth are necessary. The results also show
interesting aspects of granular dynamics which are briefly presented, like
extensive p-mode ridges in the k- diagram and a ringlike distribution
of horizontal vorticity around granules. At large scales, the horizontal
velocity is much larger than the vertical velocity and the vertical motion is
dominated by p-mode oscillations.Comment: Contribution to the proceedings of the workshop entitled "THEMIS and
the new frontiers of solar atmosphere dynamics" (March 2001), 6 pages, to
appear in Nuovo Cimento
Balltracking: an highly efficient method for tracking flow fields
We present a method for tracking solar photospheric flows that is highly efficient, and demonstrate it using high resolution MDI continuum images. The method involves making a surface from the photospheric granulation data, and allowing many small floating tracers or balls to be moved around by the evolving granulation pattern. The results are tested against synthesised granulation with known flow fields and compared to the results produced by Local Correlation tracking (LCT). The results from this new method have similar accuracy to those produced by LCT. We also investigate the maximum spatial and temporal resolution of the velocity field that it is possible to extract, based on the statistical properties of the granulation data. We conclude that both methods produce results that are close to the maximum resolution possible from granulation data. The code runs very significantly faster than our similarly optimised LCT code, making real time applications on large data sets possible. The tracking method is not limited to photospheric flows, and will also work on any velocity field where there are visible moving features of known scale length
A simulation of solar convection of supergranulation scale
We present here numerical simulations of surface solar convection which cover a box of 30Ă—30Ă—3.2 Mm3 with a resolutionof 315Ă—315Ă—82, which is used to investigate the dynamics of scales larger than granulation. No structure resembling supergranulation is present; possibly higher Reynolds numbers (i.e. higher numerical resolution), or magnetic fields, or greater depth are necessary. The results
also show interesting aspects of granular dynamics which are briefly presented, like extensive p-mode ridges inthe k-ω diagram and a ringlike distribution of horizontal
vorticity around granules. At large scales, the horizontal velocity is much larger than the vertical velocity and the vertical motion is dominated by p-mode oscillations
Characterization of horizontal flows around solar pores from high-resolution time series of images
Though there is increasing evidence linking the moat flow and the Evershed
flow along the penumbral filaments, there is not a clear consensus regarding
the existence of a moat flow around umbral cores and pores, and the debate is
still open. Solar pores appear to be a suitable scenario to test the
moat-penumbra relation as evidencing the direct interaction between the umbra
and the convective plasma in the surrounding photosphere, without any
intermediate structure in between. The present work studies solar pores based
on high resolution ground-based and satellite observations. Local correlation
tracking techniques have been applied to different-duration time series to
analyze the horizontal flows around several solar pores. Our results establish
that the flows calculated from different solar pore observations are coherent
among each other and show the determinant and overall influence of exploding
events in the granulation around the pores. We do not find any sign of
moat-like flows surrounding solar pores but a clearly defined region of inflows
surrounding them. The connection between moat flows and flows associated to
penumbral filaments is hereby reinforced by this work.Comment: 10 pages, 10 figures, Accepted for publication in Astronomy and
Astrophysics
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